Device for ventilating turbine disks in a gas turbine engine

ABSTRACT

The present invention relates to a device for ventilating turbine components in a gas turbine engine comprising two turbine rotors mechanically independent of each other, each with at least one turbine disk, an HP turbine disk and an LP turbine disk respectively, and with a first circuit for ventilating the LP turbine. The device comprises an air compression wheel arranged downstream of the HP turbine disk especially between said two turbine disks, HP and LP in order to assist the circulation of the air in said first circuit. The invention also relates to the wheel.

BACKGROUND OF THE INVENTION

The present invention relates to the field of gas turbine engines andfocuses on the circulation of the air required for the ventilation andcooling of components located downstream of the combustion chamber,especially the turbine disks.

In a gas turbine engine, it is necessary to make air circulate throughall the components subject to thermal stresses from hot gases downstreamof the combustion chamber in order to control their temperature. In atwo-cylinder engine, the air circuit for the ventilation of the highpressure section is distinct from the one for ventilating the lowpressure section located downstream, because the materials and thethermal stresses are different

The present invention relates to the low pressure section ventilationcircuit.

DESCRIPTION OF THE PRIOR ART

In a modem two-cylinder engine for civilian use, such as the CFM engine,comprising a high-pressure (HP) cylinder with an HP turbine stage 1 anda low-pressure (LP) cylinder with an LP turbine 30 with three stages 31,32 and 33, the various circuits providing ventilation downstream of thehigh-pressure turbine are illustrated in FIG. 1; the following items canbe seen:

An air flow A, drawn off from the center of the HP compressor, routedthrough the vanes of the distributor 20 of the first LP stage andproviding at A′ the purging of the downstream cavity 11 of the HPturbine 10.

A fraction A″ of this same flow providing the ventilation of thepassages in the first two fans of stages 31 and 32 of the low-pressureturbine 30.

An air flow B drawn off upstream of the HP compressor, routed throughthe passage 13 in the HP turbine 10 and providing the ventilation of thepassage in the third stage 33 of the LP turbine 30.

An air flow C drawn off at the LP compressor, routed through the passage13 in the HP turbine 10, and providing the pressurization of the covers36 of the chambers containing the bearings.

Compressors for this type of engine are axial and have sufficient spacesfor guiding the various ventilation air flows from the draw-off zone towhere they are used.

Some engines that are less powerful and more compact have an HP cylinderwith a shorter radial compressor, and their compression ratio is lower.This arrangement poses problems when it comes to providing theventilation function mentioned above.

The pressure is not always sufficient to ventilate the passages in theLP turbine disks correctly, and this situation is not helped by thesmall cross section of flow between the passage in the HP turbine andthe LP shaft.

The radial compressor centrifugal wheel has a relatively large outputdiameter. This results in a reduced gap for the air routed to the LPturbine first stage distributor. In addition, as shown in FIG. 2, thedraw-off within the HP compressor is often carried out by means ofcentripetal draw-off tubes which cause a large pressure drop in theventilation air.

The objective of the invention is to solve the abovementioned problems,by providing a means for correctly ventilating the LP turbine disks,especially in compact engines having a centrifugal compressor, whichalso takes into account the specific dimensional constraints for thistype of engine.

SUMMARY OF THE INVENTION

The invention manages to achieve this objective by means of a device forventilating turbine components in a gas turbine engine comprising twoturbine rotors that are mechanically independent of each other, each onewith at least one turbine disk, an HP turbine disk and an LP turbinedisk respectively, and with a first circuit for ventilating the LPturbine. This device is noteworthy in that it comprises an aircompression wheel arranged downstream of the HP turbine disk, inparticular between said two, HP and LP, turbine disks assisting at leastpartially the circulation of air in said first air circuit. Moreparticularly, the air inlet of the wheel connects with the passage inthe Up turbine disk, and the passage is supplied with air coming fromthe HP compressor.

Owing to the invention, the air circuits through the turbine passagesare used efficiently, and it is now also possible to simplify thestructure of the first stage distributor of the low-pressure turbinebecause it is no longer necessary to route air from it through thevanes.

According to a first embodiment, the compression wheel is connected tothe HP turbine disk. Advantageously, the wheel then becomes a structuralmember of the turbine disk by forming the bearing support. According toa second embodiment the compression wheel is connected to the LP turbinedisk.

According to another feature, the compression wheel comprises a diskprovided with radial vanes cooperating with a stator baffle in order tocompress the air. Advantageously, the baffle includes air guide vanes.

According to another feature, the stator baffle delimits with the HPturbine disk an HP turbine downstream cavity, and the air coming fromthe HP turbine disk passage partly supplies the wheel and partlysupplies the cavity.

According to another feature, the device comprises a second ventilationcircuit, said circuit ventilating the separate bearing oil chambercovers, in particular said second circuit comprises a part forming aguide channel that is coaxial with the guide part of the first circuit.

The invention also relates to an air compression wheel for the devicecomprising a radial plate with a first annular portion provided withmounting holes and a second portion provided with radial vanes.According to a first embodiment, the first portion is radially inside inrelation to the second portion. According to a second embodiment, thefirst portion is radially outside in relation to the second portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The description which follows relates to two non-limiting embodiments ofthe invention, with reference to the appended drawings, in which:

FIG. 1 illustrates in half axial cross section part of astate-of-the-art two-cylinder gas turbine engine, comprising an HPturbine and an LP turbine;

FIG. 2 illustrates in half axial cross section an engine with a radialcompressor from the prior art;

FIG. 3 illustrates in half axial cross section a turbine disk fittedwith a wheel according to the invention;

FIG. 4 illustrates in perspective view a single wheel according to theinvention; and

FIG. 5 illustrates a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, it shows what is known as a “small” two-cylindergas turbine engine. The high-pressure (HP) cylinder comprises a turbine110 connected to an HP compressor 115 by a shaft 117. The compressor 115is of the centrifugal wheel type. The low-pressure cylinder comprises alow-pressure turbine 120 with several stages mounted on a shaft 127,coaxial with the shaft 117, being connected to an axial-typelow-pressure compressor 125, itself having several stages. A combustionchamber 130 is arranged between the compressor and the BP cylinderturbine. A distributor stage 140 separates the two turbines 110 and 120.

As can be seen on this figure without the use of the invention, a firstventilation air circuit E comprises an air inlet upstream of the HPcompressor and this air is directed axially between the two shafts 117and 127 through the passage in the turbine rotor 110 in order toventilate the downstream cavity of the turbine. A second air circuit isguided between the outer casing 150 of the engine and HP cylinderhousing via tubes that are not shown. It appears that such anarrangement is not satisfactory because the quantity of air supplyingthe ventilation circuits is not sufficient.

-   -   With regard to the first circuit, the flow area between the        shafts 117 and 127 is too small for the ventilation air.    -   With regard to the second circuit, there is little space for        installing ventilation tubes on the housing.

According to the invention, there has been arranged, downstream of theHP turbine disk, an air compression wheel for ventilating the LPturbine. Such a device is illustrated in FIG. 3.

All that can be seen in this figure is the disk 210D of the HP turbine210 with a central passage 210A. The disk 210D is connected to the shaft217. At its upstream end, the shaft 217 is connected to the compressor,which is not visible in the figure. The disk carries HP turbine vanes210T receiving the hot gases from the combustion chamber not visible inthe figure.

A distributor stator stage 220 is placed downstream of the HP turbine210 immediately upstream of the vanes of the low-pressure LP turbine230.

This turbine is composed of several disks connected together, of whichonly the first two, 231 and 232, can be seen. The turbine 230 is carriedon a shaft 237. This shaft 237 is concentric with the shaft 217. Adownstream inter-shaft bearing 240 holds the two concentric shafts andallows them to rotate freely in relation to each other. The upstreambearing is not visible in the figure, the same as the downstream bearingcarrying the shaft 237 in the fixed structure. An annular space F isthus arranged between the passage 210A of the turbine disk and the shaft217. Another annular space G is also arranged between the two shafts 217and 237.

The disk 210D has a flange 210B to which is bolted a compression wheel300. The wheel has a part generally in the form of a disk atright-angles to the engine's axis, with a first portion 301 drilledaxially with a series of holes 303 for mounting bolts 303′ to passthrough for fastening the wheel to the flange 210B. Radially on theoutside of this portion, the disk has an annular portion 305 providedwith radial vanes 307. This second portion cooperates with a fixed wall222 to form a centrifugal air compressing means with an axial inlet anda radial outlet. The wall 222 carries axial compressor inlet guide vanes222A and radial compressor outlet guide vanes 222S. An annular deflector222D directs the air flow exiting the compressor toward the base of theturbine disks 231 and 232. The wall 222 makes with the turbine disk 210Da space 211 forming said HP turbine downstream cavity, and a labyrinthsealing means 222L cooperates with a corresponding means 210L on thedisk in order to confine the air in this cavity 211. Note that the wheelcomprises a cylindrical portion 309 forming a support for the outer race242 of the bearing 240. The bearing elements 244 are thereby arrangedbetween the inner race 246 connected to the shaft 237 and the outer race242 connected to the shaft 217 and form the inter-shaft bearing 240.

The flange 210B is at right-angles to a cylindrical axial part 210B1 anda perpendicular part 210B2 comprising the holes, cooperating with theholes 303 for the bolts 303′ to pass through. The cylindrical part 210B1is drilled with radial holes 210B1 r. An annular space is arrangedbetween the flange 210B, the wheel 300 and the wall 222. Radial holes222P are made in the wall 222 between the vanes 222A and the seal 222L.

Holes 309P are made in the cylindrical portion 309 of the wheel in orderto connect the space G with the downstream part of the low-pressurerotor 230.

The inventive device operates in the following manner. When the engineis operating, the two rotors, HP and LP respectively, are driven by thegases coming from the combustion chamber. Each one turns independentlyof the other. The ventilation air drawn off at the final stages of theupstream compressor according to a first circuit is guided into thespace F, and passes through the flange 210B via the holes 21OB1 r. Apart is aspirated by the wheel 300, and the other part is guided throughthe holes 222P into the downstream cavity 211 of the HP turbine that itventilates. The compressed air in the compression channels of the wheel300 is evacuated in the direction of the turbine disks 231 and 232 forwhich it provides the ventilation, and is evacuated into the combustiongas stream or via the appropriate orifices through the LP turbinesupport 230.

The ventilation air, drawn off at the primary stages of the HPcompressor, which circulates in the annular space G, between the twoshafts 217 and 237, is guided through the holes 309P toward thedownstream of the LP turbine, in particular toward the bearing oilchamber covers.

According to another embodiment, illustrated in FIG. 5, there is the HPturbine disk 210′ with a downstream flange 210B′, for mounting alabyrinth sealing member 210L′. The wheel 400 is here connected to theLP turbine disk 231′ by which it is driven. The wheel 400 as in thepreceding solution cooperates with the stator member 222′ to formcompression channels for the air which is guided through the centralpassage of the disk 210D′, the holes 210P′ made in the flange 210B′ andcoming from the upstream compressor. The air flow is split into a partwhich purges the downstream cavity 211′ of the turbine disk 210′ and apart which is drawn into the compression channels of the wheel 400. Thewheel 400 comprises openings for ventilating the turbine disks 231′ and233′.

1. A device for ventilating turbine components in a gas turbine enginecomprising two turbine rotors that are mechanically independent of eachother, each one with at least one turbine disk, an HP turbine disk andan LP turbine disk respectively, and with a first ventilation circuitfor the LP turbine, which comprises an air compression wheel arrangeddownstream of the HP turbine disk in order to assist the circulation ofair in said first circuit.
 2. The device as claimed in claim 1 whereinthe compression wheel is arranged between said two turbine disks, HP andLP.
 3. The device, as claimed in the preceding claim, wherein thecompression wheel is connected to the HP turbine disk.
 4. The device, asclaimed in claim 1, wherein the compression wheel (400) is connected tothe LP turbine disk.
 5. The device, as claimed in one of claims 1 to 4,wherein the air inlet of the wheel connects with the passage of the HPturbine disk.
 6. The device, as claimed in the preceding claim, whereinthe passage is supplied with air coming from the HP compressor.
 7. Thedevice, as claimed in any one of the preceding claims, wherein thecompression wheel comprises a disk provided with radial vanescooperating with a stator baffle in order to compress the air.
 8. Thedevice, as claimed in claim 7, wherein the baffle includes air guidevanes.
 9. The device, as claimed in either claim 7 or 8, wherein thestator baffle delimits with the HP turbine disk an HP turbine downstreamcavity.
 10. The device, as claimed in either claim 5 or 6 combined withclaim 8, wherein the air coming from the passage partly supplies thewheel and partly supplies the cavity.
 11. The device, as claimed in anyone of claims 1 to 10, comprising a second ventilation circuit, forventilating the separate bearing oil chamber covers.
 12. The device, asclaimed in claim 11, wherein said second circuit, comprises a guide partthat is coaxial with the guide part of the first circuit.
 13. A gasturbine engine, which includes a ventilation device as claimed in anyone of the preceding claims.
 14. An air compression wheel, for thedevice as claimed in any one of the preceding claims, comprising aradial plate with a first annular portion provided with mounting holesand a portion provided with radial vanes.
 15. The wheel, as claimed inclaim 14, wherein the first portion is radially inside in relation tothe second portion.
 16. The wheel, as claimed in claim 14, wherein thefirst portion is radially outside in relation to the second portion.